1. Field of the Invention
The present invention relates to an operating system of a light emitting device, and more particularly, to an operating system for estimating thermal property of a light emitting device to operate the light emitting device, and an operating method thereof.
2. Discussion of the Related Art
A light emitting diode (LED) is a semiconductor light emitting device to convert electric current into light. A red LED using a GaAsP compound semiconductor is firstly produced in 1962, and the red LED and a GaP:N based green LED are used as light sources for displays of electronic apparatuses including information and telecommunication equipments.
The wavelength of light emitted from the LEDs is dependent on semiconductor material used to manufacture the LEDs. This is because the wavelength of the emitted light depends on a band-gap of the semiconductor material, indicating an energy difference between valence band electrons and conduction band electrons.
A gallium nitride (GaN) compound semiconductor is spotlighted in the field of developing a high-output electronic device due to the high thermal stability and the broad band gap (0.8 eV to 6.2 eV). One of reasons why the GaN compound semiconductor is spotlighted is that GaN is combined with other elements such as indium (In), aluminum (Al), and the like to form semiconductor layers to emit green light, blue light, and white light.
As described above, since the emission wavelength can be adjusted, properties of materials can be adjusted in accordance with the property of a specific device. For example, GaN is used to fabricate a white LED capable of replacing the blue LED and an incandescent lamp useful in the optical recording.
Moreover, the conventional green LED is implemented by GaP in the early stage. Since GaP has a low efficiency as an indirect transition material, it is impossible to emit a pure green light. As the growth of InGaN thin films is succeeded, it is possible to implement a high-brightness green LED.
Due to the above-described advantages and other advantages, markets for the GaN based LEDs is rapidly developed. Thus, technologies relating to the optoelectronic devices are also rapidly developed since 1994 when the GaN based LEDs are commercially introduced.
Since the efficiency of the GaN light emitting diode is superior to that of the incandescent lamp, and is substantially equal to that of a fluorescent lamp now, there is an expectation that the market for the GaN based LED continuous the rapid growth.
As such, the LEDs are used in various fields such as a traffic light, a vehicle, a display, and the like, the brightness is remarkably enhanced to 60 μm/W.
Moreover, according to another advantage of the LED, various colors can be implemented, a prompt driving is possible, the lifespan is 100 thousand hours, and there is no risk of explosion.
Due to the above-mentioned advantages, the majority of illumination devices are anticipated to be replaced with the LED within 10 years in the future.
Particularly, almost colors can be expressed using the three primary colors of light in comparison to other illumination devices. Moreover, in the red light R, the green light G, and the blue light B, as illustrated in FIG. 1, the frequencies and wavelengths of the LEDs are obviously districted in comparison to the wavelengths of FIG. 2.
In other words, the lamp contains spectrums such as ultraviolet rays UV or infrared rays IR, but the LED light source has a pure wavelength.
As the illuminance of the LED is remarkably enhanced, the optical efficiency is expected to be significantly increased.
However, presently, in comparison to the fluorescent lamp or the lamp having an efficiency of 30 μm/W to 100 lm/W, the red LED has about 40 lm/W, the green LED has about 20 lm/W, and the blue LED has about 8 lm/W.
In order to increase the optical efficiencies of the LEDs to that of other lamp, a high efficiency and a high driving current are required. However, the high driving current causes more power consumption. Thus, when a high brightness LED is driven, temperature of the LED chip is very high.
As such, the LED, the application range of which is widely increased in the display field today, is repeatedly turned on and off few tens to few hundreds for a second for the implementation of an image.
Thus, this duty operation must be considered when designing a driving design relating to the temperature of the LED.
The LED is a semiconductor device to convert electric energy into a light energy. Thus, the LED has the property of the semiconductor as it is, and as a result, the principal properties of the LED such as the brightness, the lifespan, a voltage, and the like are remarkably varied according to temperature.
Accordingly, prior to design of a product and the application of the LED, it is required a method of precisely estimate temperature of a chip to emit light as a core part of the LED.